macOS 12 hasn't been tried by anyone. The driver has only run on Darwin 24 and 25 (macOS 15 and 26). It depends on IONetworkingFamily and IOPCIFamily only, so it may load on 12, but I can't tell you it works.
Two things in your setup can't work on 12 either way. MtkWlanNative, the Wi-Fi menu part, is built for two Tahoe builds (25G241 and 25G332) and refuses to load anywhere else, so take it out and remove mtkfe=native mtknativeif=1 from boot-args. With the driver alone there's no Wi-Fi menu: the card shows up as an Ethernet port and you join with the mtkwifi tool. So the dead Wi-Fi icon and the Settings crash come from something else that says it's a Wi-Fi device. Is an itlwm or AirportItlwm left over from the AC 9260?
To see what the driver did:
kmutil showloaded | grep -i -E 'mtk|itlwm|bluetool'
ioreg -r -c MtkWlan -l -w0 | head -60
log show --last boot --predicate 'eventMessage CONTAINS "MtkWlan"' | tail -80
For Bluetooth, MtkBt needs BlueToolFixup, and the card's USB port has to be in your USB map. ioreg -rc MtkBt -l | grep MtkBt shows how far it got.
A minimum version is a fair idea. The README names 15 and 26 as tested, and I'd rather see your output before I set a hard limit.